ROLE OF BICAUDAL-D IN PATTERNING THE DROSOPHILA EGG CHAMBER IN MID-OOGENESIS

The Bicaudal-D (Bic-D) gene is required early in Drosophila oogenesis for the differentiation of an oocyte from one of a cluster of 16 inter connected germarial cells, To analyze the role of Bic-D later in oogen esis, we have constructed Drosophila lines in which Bic-D expression i s under the control of the hsp70 promoter, In these flies, Bic-D activ ity can be induced early in oogenesis, allowing an oocyte to be made. Then, by shifting females to noninducing conditions, Bic-D levels are depleted for the remainder of oogenesis, Using this system, we find th at Bic-D is indeed required in the later stages of oogenesis. In ovari es from mutant females, oocyte growth is reduced, apparently due to de fects in nurse-cell-to-oocyte transport. Smaller oocyte size results i n the misalignment of follicle cells and the underlying germ line, lea ding to ventralization of dorsal follicle cells and to defects in cent ripetal cell migration. In addition, we show that Bic-D is required fo r the localization of specific mRNAs at both the anterior and posterio r of the oocyte.